Surface acoustic wave device, method of manufacturing the device, and electronic component using the device and method

ABSTRACT

A surface acoustic wave (SAW) device includes a comb-shaped electrode  2,  a reflector  3  and a plurality of auxiliary electrodes  6   a  and  6   b  for surrounding the comb-shaped electrode  2  and the reflector  3,  which are electrically independent of each other and have different widths locally. The SAW device is capable of efficiently and electrically uniformizing electric charge generated by pyroelectric property of a piezoelectric substrate  1.

TECHNICAL FIELD

The present invention relates to a surface acoustic wave (SAW) device,its manufacturing method and an electronic component employing the same.

BACKGROUND ART

In a conventional SAW device, after a metallic thin film has been formedon a whole surface of a piezoelectric substrate, a resist is coated onthe metallic thin film and then, a desired electrode pattern is formedin which desired interdigital transducers and grating reflectors are notonly surrounded by dicing lines but connected by thin lines throughexposure, development and etching. The thus obtained article is cutalong the dicing lines into a plurality of the SAW devices.

In this method, once the SAW device has been cut from the piezoelectricsubstrate, the interdigital transducers and the grating reflectors areelectrically separated from each other. Hence, upon application of heator strain to the SAW device, electric charge is generated bypyroelectric property of the piezoelectric substrate. Thus, if electriccharge becomes nonuniform among the electrodes, electric dischargeoccurs between the confronting interdigital transducers, between theconfronting grating reflectors and between the interdigital transducerand the grating reflector, thereby resulting in damage to the electrodesor deterioration of characteristics of the SAW device.

On the other hand, a method for solving this problem is known fromJapanese Patent Laid-Open Publication No. 11-298289 (1999). Namely,since inside a dicing line, a short-circuiting thin line of a metallicthin film surrounds an interdigital transducer and a grating reflectorand a plurality of thin lines are provided for electrically connectingthe short-circuiting thin line of the metallic thin film and theinterdigital transducer are provided, generated electric charge isuniformized electrically, so that damage and deterioration of electricalcharacteristics due to electrostatic discharge are prevented.

However, in this conventional arrangement in which inside the dicingline, the short-circuiting thin line of the metallic thin film surroundsthe interdigital transducer and the grating reflector and the thin lineselectrically connect the short-circuiting thin line of the metallic thinfilm and the interdigital transducer, such disadvantages are incurredthat since generated electric charge cannot be neutralized anduniformized sufficiently due to rise of impedance between lines in casethe generated electric charge is large, in case a distance between theelectrodes is short, in case the connected electrodes are far from eachother, the line for connecting the short-circuiting thin line of themetallic thin film and the interdigital transducer is thin or in casethe connecting line is a meander line or a portion of the connectingline is thinner than the remaining portion of the connecting line,damage to the electrodes and deterioration of electrical characteristicsare caused by electrostatic discharge generated between the electrodes.

DISCLOSURE OF INVENTION

The present invention has for its object to provide, with a view toeliminating the drawbacks of prior art, a surface acoustic wave (SAW)device which efficiently uniformizes electric charge generated in apiezoelectric substrate by strain or heat treatment and uniformizespotential even after cutting of the substrate into a plurality of theSAW devices so as to prevent damage to electrodes and deterioration ofelectrical characteristics, its manufacturing method and an electroniccomponent employing the SAW device.

In order to accomplish this object of the present invention, the presentinvention has the following arrangements.

In an arrangement of claim 1, a comb-shaped electrode and a reflectorare surrounded by a plurality of auxiliary electrodes, which areelectrically independent of each other and have different widthslocally. By this arrangement, since electric charge generated by heattreatment, etc. can be uniformized efficiently and electrically, localnonuniformity of produced potential is lessened, so that such an effectis gained that breakdown of the device due to electrostatic discharge,etc. can be eliminated.

In an arrangement of claim 2, the auxiliary electrodes are each used asa ground electrode. By this arrangement, if the auxiliary electrodes areconnected to a ground of a substrate having the SAW device mountedthereon, etc., an electrically uniform ground having a larger area canbe obtained, so that local nonuniformity of produced potential islessened and thus, such an effect is achieved that breakdown of thedevice due to electrostatic discharge, etc. can be eliminated.

In an arrangement of claim 3, the auxiliary electrodes are disposedsubstantially equivalently. By this arrangement, since electric chargegenerated at respective portions can be uniformized substantiallyequally and electrically, local nonuniformity of produced potential islessened, so that such an effect is obtained that breakdown of thedevice due to electrostatic discharge, etc. can be eliminated.

In an arrangement of claim 4, a beltlike input terminal lead-outelectrode and a beltlike output terminal lead-out electrode are eachconnected to the comb-shaped electrode and an input terminal electrodeand an output terminal electrode are, respectively, connected to theinput terminal lead-out electrode and the output terminal lead-outelectrode. By this arrangement, since electric charge generated at theinput terminal lead-out electrode, the output terminal lead-outelectrode, the input terminal electrode and the output terminalelectrode can be uniformized, local nonuniformity of produced potentialis lessened, so that such an effect is gained that breakdown of thedevice due to electrostatic discharge, etc. can be eliminated.

In an arrangement of claim 5, the input terminal lead-out electrode andthe output terminal lead-out electrode confront each other and are madesubstantially equal in area, while the input terminal electrode and theoutput terminal electrode confront each other and are made substantiallyequal in area. By this arrangement, since electric charge generated atan input terminal lead-out electrode portion and an output terminallead-out electrode portion can be made substantially equal so as to beuniformized electrically, local nonuniformity of produced potential islessened, so that such an effect is achieved that breakdown of thedevice due to electrostatic discharge, etc. can be eliminated.

In an arrangement of claim 6, at least a portion of the reflector iselectrically connected to the auxiliary electrodes. By this arrangement,since electric charge generated at the reflector can be uniformized overthe electrodes as a whole through the auxiliary electrodes, localnonuniformity of produced potential is lessened, so that such an effectis obtained that breakdown of the device due to electrostatic discharge,etc. can be eliminated.

In an arrangement of claim 7, the reflector is electrically connected toeach of the auxiliary electrode by a linear or beltlike electrode. Bythis arrangement, since generated electric charge can be uniformizedefficiently, local nonuniformity of produced potential is lessened, sothat such an effect is gained that breakdown of the device due toelectrostatic discharge, etc. can be eliminated.

In an arrangement of claim 8, the reflector is set in an electricallyopen state relative to the auxiliary electrodes. By this arrangement,since the auxiliary electrodes are least likely to be influenced bypotential change, local nonuniformity of produced potential is lessened,so that such an effect is achieved that breakdown of the device due toelectrostatic discharge, etc. can be eliminated.

In an arrangement of claim 9, the reflector is formed by a meander lineand is electrically connected to the comb-shaped electrode. By thisarrangement, since the reflector and the comb-shaped electrode can beset at an identical potential, local nonuniformity of produced potentialis lessened, so that such an effect is obtained that breakdown of thedevice due to electrostatic discharge, etc. can be eliminated.

A method of claim 10 includes the steps of providing on a piezoelectricsubstrate at least one set of a comb-shaped electrode, a reflector, aplurality of auxiliary electrodes for surrounding the comb-shapedelectrode and the reflector, which are electrically independent of eachother and have different widths locally, an input terminal electrode, aninput terminal lead-out electrode, an output terminal electrode and anoutput terminal lead-out electrode and cutting the substrate alongportions between neighboring ones of the auxiliary electrodes. By thismethod, since electric charge generated in the piezoelectric substratecan be uniformized, local nonuniformity of produced potential islessened, so that such an effect is gained that breakdown of the devicedue to electrostatic discharge, etc. can be eliminated.

In a method of claim 11, at least an uppermost layer of the inputterminal electrode, the output terminal electrode and the auxiliaryelectrodes is formed by deposition. By this method, such an effect isachieved that connection of these electrodes to an external terminal canbe stabilized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top plan view showing an arrangement of an electrode patternof a SAW device according to a first embodiment of the presentinvention.

FIG. 2 is a top plan view showing an arrangement of a plurality of theelectrode patterns of the SAW device of FIG. 1 formed on a wafer.

FIG. 3 is a sectional view of an electronic component employing the SAWdevice of FIG. 1.

FIG. 4 is a top plan view showing an arrangement of an electrode patternof a SAW device according to a second embodiment of the presentinvention.

FIG. 5 is a top plan view showing an arrangement of an electrode patternof a SAW device according to a third embodiment of the presentinvention.

FIG. 6 is a top plan view showing an arrangement of an electrode patternof a SAW device according to a fourth embodiment of the presentinvention.

FIG. 7 is a top plan view showing an arrangement of a plurality of theelectrode patterns of the SAW device of FIG. 6 formed on a wafer.

FIG. 8 is a sectional view of an electronic component employing the SAWdevice of FIG. 6.

FIG. 9 is a top plan view showing an arrangement of an electrode patternof a SAW device according to a fifth embodiment of the presentinvention.

FIG. 10 is a top plan view showing an arrangement of an electrodepattern of a SAW device according to a sixth embodiment of the presentinvention.

FIG. 11 is a top plan view showing an arrangement of an electrodepattern of a SAW device according to a seventh embodiment of the presentinvention.

FIG. 12 is a top plan view showing an arrangement of an electrodepattern of a SAW device according to an eighth embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment)

Hereinafter, Claims 1 to 5, 8 and 10 to 15 of the present invention aredescribed by utilizing a first embodiment of the present invention. FIG.1 is a top plan view showing an arrangement of an electrode pattern of asurface acoustic wave (SAW) device 10A according to the first embodimentof the present invention and FIG. 2 is a top plan view showing anarrangement of a plurality of the electrode patterns of FIG. 1 formed ona wafer. Meanwhile, FIG. 3 is a sectional view of an electroniccomponent 40A in which the SAW device 10A is sealed in a package, etc.“1” is a piezoelectric substrate, “2” is a comb-shaped electrode, “3” isa reflector, “4 a” is an input terminal lead-out electrode, “4 b” is aninput terminal electrode, “5 a” is an output terminal lead-outelectrode, “5 b” is an output terminal electrode, “6 a” and “6 b” areauxiliary electrodes which are electrically independent of each otherand have different widths locally, “7” is a bump, “8” is a regiondisposed between the auxiliary electrodes 6 a and 6 b and “18” is abeltlike electrode.

Meanwhile, FIGS. 1 to 3 show an arrangement of the first embodimentschematically and do not illustrate relative ratio of respectivedimensions.

A piezoelectric substance generates electric charge by pyroelectricproperty upon application of heat or strain thereto. In thepiezoelectric substance, if electric charge varies locally, potentialdifference is produced so as to induce electrostatic discharge, therebyresulting in breakdown of a device or deterioration of electricalcharacteristics. In order to prevent such a phenomenon, it is effectiveto make the potential identical as rapidly as possible by eliminatingthe produced potential difference.

In order to make the produced potential identical as much as possible soas to acquire balance of the potential in the SAW device 10A, thepresent invention has found that it is effective to providelow-impedance portions as widely as possible in a circuit pattern of theSAW device 10A. Namely, in the electrode pattern of the SAW device 10Aof the present invention, the comb-shaped electrode 2 and a pair of thereflectors 3 which are disposed at opposite sides of the comb-shapedelectrode 2 closely to a propagation direction of a surface wavegenerated from the comb-shaped electrode 2 are provided on thepiezoelectric substrate 1, while the comb-shaped electrode 2 and thereflectors 3 are surrounded by a plurality of the auxiliary electrodes 6a and 6 b which are electrically independent of each other and havedifferent widths locally.

A plurality of the auxiliary electrodes 6 a and 6 b are connected to aground of an external circuit such as the substrate 1 having the SAWdevice 10A mounted thereon. In each SAW device 10A, the auxiliaryelectrodes 6 a and 6 b are disposed substantially equivalently, forexample, substantially symmetrically with respect to a point,substantially symmetrically with respect to a plane and substantiallysymmetrically with respect to a line so as to least deviate from eachother. In addition, the beltlike input terminal lead-out electrode 4 aconnected to the comb-shaped electrode 2, the input terminal electrode 4b, the beltlike output terminal lead-out electrode 5 a and the outputterminal electrode 5 b are provided. The beltlike input terminallead-out electrode and output terminal lead-out electrode 4 a and 5 aconfronting each other are made substantially equal in area and theinput terminal electrode 4 b and the output terminal electrode 5 bconfronting each other are made substantially equal in area.Furthermore, the reflector 3 and the auxiliary electrodes 6 a and 6 bare set in an electrically open state so as to have an electrodearrangement in which the comb-shaped electrodes 2 are connected to eachother by the beltlike electrode 18.

Meanwhile, the beltlike input terminal lead-out electrode 4 a and thebeltlike output terminal lead-out electrode 5 a are arranged to beconnected to input terminal electrode 4 b and the output terminalelectrode 5 b, respectively.

Meanwhile, since the input terminal lead-out electrode 4 a and theoutput terminal lead-out electrode 5 a confront each other so as to havea substantially identical area and the input terminal electrode 4 b andthe output terminal electrode 5 b confront each other so as to have asubstantially identical area, balance of generated electric charge canbe readily acquired and thus, potential can be made uniform effectively.However, for example, if these electrodes cannot be provided so as toconfront each other due to layout of the electrode pattern, the sameeffect as those of the case in which the electrodes confront each othercan be gained when the electrodes are disposed as equivalently aspossible by making the electrodes substantially symmetrical with respectto a line or substantially symmetrical with respect to a point.

The auxiliary electrodes 6 a and 6 b are made as wide as circuit designpermits for minimizing the impedance and uniformizing potential. Theauxiliary electrodes 6 a and 6 b are apparently different from thinlines in that the auxiliary electrodes 6 a and 6 b have different widthslocally and have an expanse in area.

Thus, since the comb-shaped electrode 2 and the reflector 3 aresurrounded by the auxiliary electrodes 6 a and 6 b, the auxiliaryelectrodes 6 a and 6 b can be made wider than the thin lines and madesmaller in impedance between lines and in a plane than the thin lines,so that potential produced by storage of electric charge generated bypyroelectric property of the piezoelectric substrate 1 can be madeuniform rapidly in a wider region than the thin lines and thus, the SAWdevice 10A can be made uniform electrically.

Meanwhile, since the auxiliary electrodes 6 a and 6 b are connected tothe ground of the external circuit such as the substrate 1 having theSAW device 10A mounted thereon so as to be used as ground electrodes ofthe SAW device 10A, the auxiliary electrodes 6 a and 6 b can act asgrounds electrically common with a ground of a larger external circuit,so that change of potential can be made more rapidly and more uniformlyand thus, influence of electric charge generated by pyroelectricproperty of the piezoelectric substrate 1 can be lessened.

Potential difference of the SAW device 10A is produced by electriccharge generated by pyroelectric property of the piezoelectric substrate1 upon application of heat or strain thereto. In an ordinary state ofmanufacture, electric charge is not generated locally but is generatedfrom the SAW device 10A as a whole. Generally, in SAW devices, input andoutput electrodes to be connected to bumps, etc. have largest areas andelectric charge is generated quite readily from the input and outputelectrodes.

Meanwhile, FIGS. 1 and 2 show the arrangement of the SAW device 10Aschematically and do not illustrate relative ratio of sizes ofconstituent elements. Therefore, if a common electrode portion having aslarge an area as possible is provided at a portion which surrounds afunctional portion including the comb-shaped electrode 2 and thereflector 3 so as to have the input terminal electrode 4 b and theoutput terminal electrode 5 b at its center, potential can be equalizedby uniformizing the generated electric charge efficiently and occurrenceOT electrostatic discharge, etc. can be restrained.

Meanwhile, in order to prevent damage to a device due to electrostaticdischarge, there are, for example, a method in which a narrow intervalportion is preliminarily provided between neighboring electrodes andperforms, upon storage of electric charge to some extent, electrostaticdischarge partially in such a range as to prevent damage to the deviceand a method in which nonuniformity itself of potential causing staticelectricity is restrained. In the method in which electrostaticdischarge is performed partially, electric discharge is repeated uponstorage of electric charge and thus, it is difficult to obtain a stablestate. Meanwhile, in the method in which nonuniformity itself ofpotential is restrained, electric charge generated from thepiezoelectric substrate 1 is not made nonuniform locally by providingthe common electrode portion having as large the area as possible, sothat potential is equalized and thus, the cause of electrostaticdischarge can be removed perpetually.

Therefore, in order to restrain electrostatic discharge, it is moreeffective to prevent electrostatic discharge by providing the commonelectrode portion having as large the area as possible in order to widenportions of the equal potential by the comb-shaped electrode 2, thereflector 3 and the auxiliary electrodes 6 a and 6 b than to causeelectrostatic discharge on purpose by controlling the interval betweenthe electrodes.

From the above, it is desirable that the number of division of theauxiliary electrodes 6 a and 6 b is essentially smaller. However, evenin case the electrodes should be divided due to layout of externalterminals, the generated electric charge can be uniformized efficientlyand occurrence of electrostatic discharge, etc. can be restrained in thearrangement of the present invention.

Meanwhile, in the SAW device 10A, if areas of the beltlike inputterminal lead-out electrode and output terminal lead-out electrode 4 aand 5 a are made substantially equal to each other and areas of theinput terminal electrode 4 b and the output terminal electrode 5 b aremade equal to each other, while the auxiliary electrodes 6 a and 6 bwhich are electrically independent of each other and are short-circuitedin plane are disposed equivalently so as to be well balanced as a whole,a location where a large quantity of electric charge is stored locallycan be eliminated and thus, potential can be made more uniform.

Since the auxiliary electrodes 6 a and 6 b are disposed equivalently soas to be well balanced as a whole, electric charge generated in thereflector 3 can be uniformized even when the reflector 3 is in anelectrically open state relative to the auxiliary electrodes 6 a and 6b, so that local potential difference does not occur and thus, breakdownof the device or deterioration of electrical characteristics can beeliminated.

Meanwhile, the same effects can be achieved even when a plurality ofsets of the comb-shaped electrode 2 and/or the reflector 3 are provided.

The SAW device 10A of the present invention is manufactured as follows.By using a sputtering apparatus (not shown), a metallic thin film of Tiis formed on a piezoelectric substrate 1 made of LiTaO₃ or the like.Then, a metallic thin film of Al—Sc—Cu or Ti is formed on the metallicthin film of Ti by using a sputtering apparatus (not shown).Furthermore, by using a deposition apparatus (not shown), a metallicthin film of Al is formed on the input terminal lead-out electrode 4 aand the output terminal lead-out electrode 5 a. In addition to Al—Sc—Cuand Ti, other metals or alloys may also be used, in accordance withpurposes, as materials of the metallic thin films formed by sputtering.At least one metallic thin film, namely, a plurality of the metallicthin films may be laminated on one another in accordance with thepurposes and order of lamination of the metallic thin films may bechanged in accordance with the purposes.

Then, a resist is coated on the metallic thin film and exposure isperformed with a stepper (not shown) by setting a desired photomask tothe resist. Subsequently, an exposed portion of the resist is developedby using a developing apparatus (not shown) and an unnecessary portionof the resist is removed. Furthermore, a desired electrode pattern isformed on the metallic thin film by using a dry etching apparatus (notshown) or the like.

After the remaining resist has been removed, resist is coated on theelectrode pattern again and exposure is performed with a stepper (notshown) by setting a desired photomask to the resist. Subsequently, anexposed portion of the resist is developed by using a developingapparatus (not shown) and an unnecessary portion of the resist isremoved. Thereafter, a metallic thin film of Al or the like is formed byusing a deposition apparatus (not shown) so as to form a deposited filmof Al on the input terminal electrode 4 b and the output terminalelectrode 5 b and the remaining resist is removed.

Meanwhile, in addition to the above described method of forming thedesired electrode pattern, another method, for example, may be employedin which after a desired metallic thin film has been formed, the desiredelectrode pattern is formed on the metallic thin film at a time by usinga dry etching apparatus (not shown).

Then, by using a dicing apparatus (not shown) or the like, the thusobtained article is cut along dicing lines into a plurality of the SAWdevices 10A.

Meanwhile, supposing that “λ” denotes a wavelength of an operatingfrequency of the SAW device 10A, a width of the auxiliary electrodes 6 aand 6 b in the electrode pattern employed in the first embodiment is inthe range of λ/4 to 100λ but may be in other ranges than the aboverange.

Subsequently, the electronic component 40A is assembled by using thethus obtained SAW device 10A. FIG. 3 is a sectional view of theelectronic component 40A employing the SAW device 10A. “9” is a basemember, “10A” is the SAW device, “11” is a bump, “12” is a pad, “13” isa lead-out electrode, “14” is a terminal electrode, “15” is a cover and“16” is a bonding member.

The bump 11 made of gold or the like is formed on the pad 12 of the SAWdevice 10A. Then, the SAW device 10A formed with the bump 11 is providedon the base member 9 having the lead-out electrode 13 and the terminalelectrode 14 preliminarily such that the bump 11 comes into contact withthe lead-out electrode 13, so that the bump 11 is bonded to the lead-outelectrode 13 by ultrasonic wave or the like so as to be mounted thereon.

Thereafter, by using a sealing apparatus (not shown), the base member 9having the SAW device 10A and the cover 15 bearing preliminarily thebonding member 16 such as solder are provided so as to cause the bondingmember 16 to confront the base member 9 and are heated and sealed, sothat the electronic component 40A is obtained.

In addition to the above described method of manufacturing theelectronic component 40A, another method, for example, wire bonding maybe used as necessary for mounting and gold or brazing filler metalcontaining gold, for example, may be used as the bonding member 16.

Meanwhile, in comparison with wire bonding, bump bonding can increasearea of its contact with the electrode to be bonded thereto andtherefore, can raise bonding reliability. On the other hand, in casestrain produced at the time of bump bonding remains at the electrodeheld in contact with the bump, the electrodes may be separated from eachother, thus resulting in drop of bonding reliability contrarily.

The present invention has found that when the metallic thin film isformed by deposition, strain at the time of bump bonding, electricalcorrosion and corrosion at the time of cutting are less likely to beproduced than sputtering. This reason is considered that sputteringmerely piles metallic particles on one another physically, while indeposition, formation of a thin film having orientation identical withcrystalline orientation strengthens coupling between metallic particles.Therefore, if at least an uppermost layer of the electrode brought intocontact with the bump is formed by deposition at the time of bumpbonding, reliability of bonding is raised by restraining occurrence ofstrain due to bonding and electrical corrosion due to bonding betweendifferent metals can be restrained. The metallic thin film formed bydeposition has better bonding property relative to the bump when made ofsofter metal and therefore, is desirably made of, for example, aluminumor aluminum-copper alloy.

Meanwhile, the same effects can be obtained when an additional layer isformed on the uppermost layer of the electrode brought into contact withthe bump. Meanwhile, if the electrode is formed by piling pieces made ofnot less than one metal, for example, Al, Ti, Cu, Cr and Ni or alloy ofthese metals, respectively, withstand power is raised. Thus, if theuppermost layer of the electrode is formed on a pile of pieces made of aplurality of the metals, respectively, it is possible to obtain anelectrode in which occurrence of bonding strain is restrained andwithstand power is raised.

Meanwhile, in the first embodiment, the auxiliary electrodes 6 a and 6 bare split into two portions but may be split into any plural portions.The bump may be formed at other locations than that indicated in thefirst embodiment. Width of the beltlike input terminal lead-outelectrode and output terminal lead-out electrode 4 a and 5 a may befixed or variable.

Since the comb-shaped electrode 2 of the thus obtained SAW device 10A isconnected to only the input terminal lead-out electrode 4 a, the inputterminal electrode 4 b, the output terminal lead-out electrode 5 a, theoutput terminal electrode 5 b and the beltlike electrode 18 connectingthe comb-shaped electrodes 2, electrical characteristics of the SAWdevice 10A can be measured in advance by electrically connecting aproper terminal to the SAW device 10A. Namely, since electricalcharacteristics of the SAW device 10A can be measured in a wafer statepreliminarily, only conforming articles can be used at a subsequentprocess by selecting characteristics prior to dicing of the wafer into aplurality of the SAW devices 10A.

In accordance with the present invention as is clear from the foregoing,since the comb-shaped electrode 2 and the reflector 3 are surrounded bythe auxiliary electrodes 6 a and 6 b which are electrically independentof each other and have different widths locally and the uppermost layerof the electrode brought into contact with the bump at least is formedby deposition, such effects that the excellent SAW device 10D can besimply manufactured are gained in which potential produced bypyroelectric property of the piezoelectric substrate 1 can beuniformized more rapidly and more simply, bonding property of theelectrodes is upgraded, corrosion due to bonding of different metals isrestrained, withstand power is raised, while breakdown of the device anddeterioration of characteristics due to electrostatic discharge or thelike are eliminated.

(Second Embodiment)

Hereinafter, Claims 1 to 7 and 10 to 15 are described by utilizing asecond embodiment of the present invention. FIG. 4 is a top plan viewshowing an arrangement of an electrode pattern of a SAW device 10Baccording to the second embodiment of the present invention. In FIG. 4,parts identical with those of FIG. 1 in the first embodiment aredesignated by identical reference numerals and the detailed descriptionis abbreviated for the sake of brevity. Meanwhile, FIG. 4 shows anarrangement of the second embodiment schematically and does notillustrate relative ratio of respective dimensions.

FIG. 4 of the second embodiment is different from FIG. 1 of the firstembodiment in that in FIG. 4, the reflector 3 is electrically connectedto the auxiliary electrodes 6 a and 6 b by a plurality of beltlikeelectrodes 17 and the three comb-shaped electrodes 2 are provided foreach of input and output terminals such that the two comb-shapedelectrodes 2 disposed at opposite ends of the three comb-shapedelectrodes 2 not only are connected to each other by the beltlikeelectrode 18 but are each connected to each of the auxiliary electrodes6 a and 6 b by a beltlike electrode 20.

Namely, in the first embodiment, the reflector 3 is in an electricallyopen state relative to the auxiliary electrodes 6 a and 6 b. On theother hand, in the second embodiment, the comb-shaped electrode 2, thereflector 3 and the auxiliary electrodes 6 a and 6 b are electricallyconnected to one another by a plurality of the beltlike electrodes 17,18 and 20. In other respects, the SAW device 10B and an electroniccomponent 40B (FIG. 3) are manufactured in the same manner as the firstembodiment.

In FIG. 4, since the comb-shaped electrode 2 and the reflector 3 areelectrically connected to the auxiliary electrodes 6 a and 6 b by aplurality of the beltlike electrodes 17 and 20 and a plurality of setsof the comb-shaped electrodes 2 are electrically connected to each otherby the beltlike electrode 18, electric charge generated in thecomb-shaped electrode 2, the reflector 3, etc. is delivered to theauxiliary electrodes 6 a and 6 b via a plurality of the beltlikeelectrodes 17, 18 and 20, so that potential can be uniformized, as awhole, over the wide electrodes including the auxiliary electrodes 6 aand 6 b.

Namely, since the comb-shaped electrode 2 and the reflector 3 areconnected to the auxiliary electrodes 6 a and 6 b by a plurality of thebeltlike electrodes 17 and 20, the wider electrodes including thecomb-shaped electrode 2 and the reflector 3 can act as a commonelectrode, so that the generated electric charge can be uniformized overa wider area so as to equalize potential. In addition, by connecting thecomb-shaped electrode 2 and the reflector 3 to the wide electrodes,impedance can be reduced in comparison with an electrically open state.

Meanwhile, effects gained by electrically connecting the reflector 3 tothe auxiliary electrodes 6 a and 6 b vary according to design of theelectrode pattern. If the electrodes capable of uniformizing potentialcan be connected at low impedance, the electrodes may be linear orplanar and the number of the electrodes may be arbitrary. However, it ismore effective that the electrodes are desirably planar and the numberof the electrodes is large.

Meanwhile, in case the reflectors 3 are electrically connected to theauxiliary electrodes 6 a and 6 b by lines, it is not preferable that ahigh-impedance portion is present in the course of connection paths.Hence, it is desirable that the line width is constant or becomessmaller towards an outer peripheral portion.

Therefore, in comparison with the first embodiment, since thecomb-shaped electrode 2, the reflector 3 and the auxiliary electrodes 6a and 6 b are connected to one another by a plurality of the beltlikeelectrodes 17, 18 and 20, the wider electrodes including the comb-shapedelectrode 2 and the reflector 3 can act as the common electrode, so thatthe generated electric charge can be uniformized over a wider area so asto equalize potential. Hence, since influence of potential due to thegenerated electric charge can be lessened further, such effects that theexcellent SAW device 10B can be simply manufactured are achieved inwhich breakdown of the device and deterioration of characteristics dueto electrostatic discharge or the like are eliminated.

Meanwhile, in FIG. 4, “21 a” denotes a ground terminal lead-outelectrode and “21 b” denotes a ground terminal electrode.

(Third Embodiment)

Hereinafter, Claims 1 to 5 and 9 to 15 of the present invention aredescribed by utilizing a third embodiment of the present invention. FIG.5 is a top plan view showing an arrangement of an electrode pattern of aSAW device 10C according to the third embodiment of the presentinvention. In FIG. 5, parts identical with those of FIG. 1 in the firstembodiment are designated by identical reference numerals and thedetailed description is abbreviated for the sake of brevity. FIG. 5 ofthe third embodiment is different from FIG. 1 of the first embodiment inthat in FIG. 5, the reflector 3 is formed by a meander line and iselectrically connected to the comb-shaped electrode 2. Meanwhile, FIG. 5shows an arrangement of the third embodiment schematically and does notillustrate relative ratio of respective dimensions.

Namely, the comb-shaped electrode 2 and the reflector 3 are set in anelectrically open state in the first embodiment, while the comb-shapedelectrode 2 and the reflector 3 are electrically connected to eachother. In other respects, the SAW device 10C and an electronic component40C (FIG. 3) are manufactured in the same manner as the firstembodiment.

In FIG. 5, a reflector 19 formed by the meander line is electricallyconnected to the comb-shaped electrode 2 and signals in use aretransmitted therebetween in DC or at low frequencies. However, in ahigh-frequency band for operating the SAW device 10C, impedance of themeander line rises and thus, the meander line is substantially set in anopen state relative to the comb-shaped electrode 2.

Meanwhile, since a common electrode portion can be enlarged byelectrically connecting the comb-shaped electrode 2 and the reflector 19formed by the meander line, electric charge generated by pyroelectricproperty of the piezoelectric substrate 1 can be uniformized over awider electrode or a longer electrode as a whole, so that potentialdifference produced at respective portions can be lessened.

Namely, since the reflector 19 formed by the meander line iselectrically connected to the comb-shaped electrode 2, the comb-shapedelectrode 2 and the reflector 3 are set in a substantially open state inthe high-frequency band so as to not only eliminate malfunctions butenlarge an electrically connected common base, so that potentialdifference produced at respective portions is lessened and thus,occurrence of electrostatic discharge, etc. can be restrained.

Therefore, in comparison with the first embodiment, such effects thatthe excellent SAW device 10C can be simply manufactured are obtained inwhich potential difference produced at respective portions including thecomb-shaped electrode 2 and the reflector 19 can be lessened further andbreakdown of the device and deterioration of characteristics due toelectrostatic discharge or the like are eliminated.

(Fourth Embodiment)

Hereinafter, Claims 16 to 20 of the present invention are described byutilizing a fourth embodiment of the present invention. FIG. 6 is a topplan view showing an arrangement of an electrode pattern of a SAW device10D according to the fourth embodiment of the present invention and FIG.7 is a top plan view showing an arrangement of a plurality of theelectrode patterns of FIG. 6 formed on a wafer. Meanwhile, FIG. 8 is asectional view showing an electronic component 40D in which the SAWdevice 10D is sealed in a package, etc.

FIG. 6 of the fourth embodiment is different from FIG. 1 of the firstembodiment in that in FIG. 6, dicing lines 28 are provided on thepiezoelectric substrate 1 of the SAW device 10D. Meanwhile, FIGS. 6 to 8show an arrangement of the fourth embodiment schematically and does notillustrate relative ratio of respective dimensions.

A piezoelectric substance generates electric charge by pyroelectricproperty upon application of heat or strain thereto. In thepiezoelectric substance, if electric charge varies locally, potentialdifference is produced so as to induce electrostatic discharge, therebyresulting in breakdown of a device or deterioration of electricalcharacteristics. In order to prevent such a phenomenon, it is effectiveto make the potential identical as rapidly as possible by eliminatingthe produced potential difference.

In order to make the produced potential identical as much as possible soas to acquire balance of the potential in the SAW device 10D, thepresent invention has found that it is effective to providelow-impedance portions as widely as possible in a circuit pattern of theSAW device 10D. Namely, in the electrode pattern of the SAW device 10Dof the present invention, the dicing lines 28 are provided on thepiezoelectric substrate 1 and inside the dicing lines 28, thecomb-shaped electrode 2 and a pair of the reflectors 3 are disposed atopposite sides of the comb-shaped electrode 2 closely to a propagationdirection of a surface wave generated from the comb-shaped electrode 2such that the comb-shaped electrode 2 and the reflectors 3 aresurrounded by the auxiliary electrodes 6 a and 6 b.

The auxiliary electrodes 6 a and 6 b are used as ground electrodes. Ineach SAW device 10D, the auxiliary electrodes 6 a and 6 b are disposedsubstantially equivalently, for example, substantially symmetricallywith respect to a point and substantially symmetrically with respect toa plane so as not to deviate from each other. In addition, the beltlikeinput terminal lead-out electrode 4 a and the beltlike output terminallead-out electrode 5 a, which are connected to the comb-shaped electrode2 are made substantially equal in area, while the input terminalelectrode 4 b and the output terminal electrode 5 b, which are connectedto the input terminal lead-out electrode 4 a and the output terminallead-out electrode 5 a, respectively are provided so as to confront eachother and are made substantially equal in area. Furthermore, thereflector 3 and the auxiliary electrodes 6 a and 6 b are set in anelectrically open state so as to have an electrode arrangement in whichthe comb-shaped electrodes 2 are connected to each other by the beltlikeelectrode 18.

Meanwhile, since the input terminal lead-out electrode 4 a and theoutput terminal lead-out electrode 5 a confront each other so as to havea substantially identical area and the input terminal electrode 4 b andthe output terminal electrode 5 b confront each other so as to have asubstantially identical area, balance of generated electric charge canbe readily acquired and thus, potential can be made uniform effectively.However, for example, if these electrodes cannot be provided so as toconfront each other due to layout of the electrode pattern, the sameeffect as those of the case in which the electrodes confront each othercan be gained when the electrodes are disposed as equivalently aspossible by making the electrodes substantially symmetrical with respectto a line or substantially symmetrical with respect to a point.

The auxiliary electrodes 6 a and 6 b are made as wide as circuit designpermits for minimizing the impedance and uniformizing potential. Theauxiliary electrodes 6 a and 6 b are apparently different from thinlines in that the auxiliary electrodes 6 a and 6 b have different widthslocally and have an expanse in area.

Thus, since the comb-shaped electrode 2 and the reflector 3 aresurrounded by the auxiliary electrodes 6 a and 6 b, the auxiliaryelectrodes 6 a and 6 b can be made wider than the thin lines and madesmaller in impedance between lines and in a plane than the thin lines,so that potential produced by storage of electric charge generated bypyroelectric property of the piezoelectric substrate 1 can be madeuniform rapidly in a wider region than the thin lines.

Meanwhile, since the auxiliary electrodes 6 a and 6 b are connected tothe ground of the external circuit such as the substrate 1 having theSAW device 10D mounted thereon so as to be used as ground electrodes ofthe SAW device 10D, the auxiliary electrodes 6 a and 6 b can act asgrounds electrically common with a ground of a larger external circuit,so that change of potential can be made more rapidly and more uniformlyand thus, influence of electric charge generated by pyroelectricproperty of the piezoelectric substrate 1 can be lessened.

Potential difference of the SAW device 10D is produced by electriccharge generated by pyroelectric property of the piezoelectric substrate1 upon application of heat or strain thereto. In an ordinary state ofmanufacture, electric charge is not generated locally but is generatedfrom the SAW device 10D as a whole. Generally, in SAW devices, input andoutput electrodes to be connected to bumps, etc. have largest areas anda largest electric charge is generated from the input and outputelectrodes.

Meanwhile, FIGS. 6 and 7 show the arrangement of the SAW device 10Dschematically and do not illustrate relative ratio of sizes ofconstituent elements.

Therefore, if a common electrode portion having as large an area aspossible is provided at a portion which surrounds a functional portionincluding the comb-shaped electrode 2 and the reflector 3 so as to havethe input terminal electrode 4 b and the output terminal electrode 5 bat its center, potential can be equalized by uniformizing the generatedelectric charge efficiently and occurrence of electrostatic discharge,etc. can be restrained.

Meanwhile, in order to prevent damage to a device due to electrostaticdischarge, there are, for example, a method in which a narrow intervalportion is preliminarily provided between neighboring electrodes andperforms, upon storage of electric charge to some extent, electrostaticdischarge partially in such a range as to prevent damage to the deviceand a method in which nonuniformity itself of potential causing staticelectricity is restrained. In the method in which electrostaticdischarge is performed partially, electric discharge is repeated uponstorage of electric charge and thus, it is difficult to obtain a stablestate. Meanwhile, in the method in which nonuniformity itself ofpotential is restrained, electric charge generated from thepiezoelectric substrate 1 is not made nonuniform locally by providingthe common electrode portion having as large the area as possible, sothat potential is equalized and thus, the cause of electrostaticdischarge can be removed perpetually.

Therefore, in order to restrain electrostatic discharge, it is moreeffective to prevent electrostatic discharge by providing the commonelectrode portion having as large the area as possible in order to widenportions of the equal potential by the comb-shaped electrode 2, thereflector 3 and the auxiliary electrodes 6 a and 6 b than to causeelectrostatic discharge on purpose by controlling the interval betweenthe electrodes.

From the above, it is desirable that the number of division of theauxiliary electrodes 6 a and 6 b is essentially smaller. However, evenin case the electrodes should be divided due to layout of externalterminals, the generated electric charge can be uniformized efficientlyand occurrence of electrostatic discharge, etc. can be restrained in thearrangement of the present invention.

Meanwhile, in the SAW device 10D, if areas of the beltlike inputterminal lead-out electrode and output terminal lead-out electrode 4 aand 5 a are made substantially equal to each other and areas of theinput terminal electrode 4 b and the output terminal electrode 5 b aremade equal to each other, while the auxiliary electrodes 6 a and 6 bwhich are electrically independent of each other and are short-circuitedin plane are disposed equivalently so as to be well balanced as a whole,a location where a large quantity of electric charge is stored locallycan be eliminated and thus, potential can be made more uniform.

Since the auxiliary electrodes 6 a and 6 b are disposed equivalently soas to be well balanced as a whole, electric charge generated in the SAWdevice 10D can be uniformized even when the reflector 3 is in anelectrically open state relative to the auxiliary electrodes 6 a and 6 bor the dicing lines 28 and the reflector 3 are in an electrically openstate, so that local potential difference does not occur and thus,breakdown of the device or deterioration of electrical characteristicscan be eliminated.

Meanwhile, by cutting the substrate 1 along the dicing lines 28,positioning for cutting can be performed easily. By providing theelectrically short-circuited dicing lines 28 at an outer peripheralportion of the SAW device 10D, generated electric charge can beuniformized effectively meanwhile, the same effects can be achieved evenwhen a plurality of sets of the comb-shaped electrode 2 and/or thereflector 3 are provided.

The SAW device 10D of the present invention is manufactured as follows.By using a sputtering apparatus (not shown), a metallic thin film of Tiis formed on a piezoelectric substrate 1 made of LiTaO₃ or the like.Then, a metallic thin film of Al—Sc—Cu or Ti is formed on the metallicthin film of Ti by using a sputtering apparatus (not shown). In additionto Al—Sc—Cu and Ti, other metals or alloys may also be used, inaccordance with purposes, as materials of the metallic thin films formedby sputtering. At least one metallic thin film, namely, a plurality ofthe metallic thin films may be laminated on one another in accordancewith the purposes and order of lamination of the metallic thin films maybe changed in accordance with the purposes.

Then, a resist is coated on the metallic thin film and exposure isperformed with a stepper (not shown) by setting a desired photomask tothe resist. Subsequently, an exposed portion of the resist is developedby using a developing apparatus (not shown) and an unnecessary portionof the resist is removed. Furthermore, a desired electrode pattern isformed on the metallic thin film by using a dry etching apparatus (notshown) or the like.

After the remaining resist has been removed, resist is coated on theelectrode pattern again and exposure is performed with a stepper (notshown) by setting a desired photomask to the resist. Subsequently, anexposed portion of the resist is developed by using a developingapparatus (not shown) and an unnecessary portion of the resist isremoved. Thereafter, a metallic thin film of Al or the like is formed byusing a deposition apparatus (not shown) so as to form a deposited filmof Al on the input terminal electrode 4 b and the output terminalelectrode 5 b and the remaining resist is removed.

In addition to the input terminal electrode 4 b and the output terminalelectrode 5 b, the deposited film of Al may also be formed as necessaryon other portions, for example, the input terminal lead-out electrode 4a, the output terminal lead-out electrode 5 a and the auxiliaryelectrode 6 short-circuited in a shape of a frame.

Meanwhile, in addition to the above described method of forming thedesired electrode pattern, another method, for example, may be employedin which after a desired metallic thin film has been formed, the desiredelectrode pattern is formed on the metallic thin film at a time by usinga dry etching apparatus (not shown).

Then, by using a dicing apparatus (not shown) or the like, the thusobtained article is cut along the dicing lines 28 into a plurality ofthe SAW devices 10D.

Meanwhile, supposing that “λ” denotes a wavelength of an operatingfrequency of the SAW device 10D, a width of the auxiliary electrodes 6 aand 6 b in the electrode pattern employed in the first embodiment is inthe range of λ/4 to 100λ but may be in other ranges than the aboverange.

Subsequently, the electronic component 40D is assembled by using thethus obtained SAW device 10D as shown in FIG. 8. In the same manner asFIG. 3, the electronic component 40D of FIG. 8 includes a base member 9,the SAW device 10D, the bump 11, the pad 12, the lead-out electrode 13,the terminal electrode 14, the cover 15 and the bonding member 16.

The bump 11 made of gold or the like is formed on the pad 12 of the SAWdevice 10D. Then, the SAW device 10D formed with the bump 11 is providedon the base member 9 having the lead-out electrode 13 and the terminalelectrode 14 preliminarily such that the bump 11 comes into contact withthe lead-out electrode 13, so that the bump 11 is bonded to the lead-outelectrode 13 by ultrasonic wave or the like so as to be mounted thereon.

Thereafter, by using a sealing apparatus (not shown), the base member 9having the SAW device 10D and the cover 15 bearing preliminarily thebonding member 16 such as solder are provided so as to cause the bondingmember 16 to confront the base member 9 and are heated and sealed, sothat the electronic component 40D is obtained.

In addition to the above described method of manufacturing theelectronic component 40D, another method, for example, wire bonding maybe used as necessary for connection to an external terminal and gold orbrazing filler metal containing gold, for example, may be used as thebonding member 16.

Meanwhile, in comparison with wire bonding, bump bonding can increasearea of its contact with the electrode to be bonded thereto andtherefore, can raise bonding reliability. On the other hand, in casestrain produced at the time of bump bonding remains at the electrodeheld in contact with the bump, the electrodes may be separated from eachother, thus resulting in drop of bonding reliability contrarily.

The present invention has found that when the metallic thin film isformed by deposition, strain at the time of bump bonding, electricalcorrosion and corrosion at the time of cutting are less likely to beproduced than sputtering. This reason is considered that sputteringmerely piles metallic particles on one another physically, while indeposition, formation of a thin film having orientation identical withcrystalline orientation strengthens coupling between metallic particles.Therefore, if at least an uppermost layer of the electrode brought intocontact with the bump is formed by deposition at the time of bumpbonding, reliability of bonding is raised by restraining occurrence ofstrain due to bonding and electrical corrosion due to bonding betweendifferent metals can be restrained. The metallic thin film formed bydeposition has better bonding property relative to the bump when made ofsofter metal and therefore, is desirably made of, for example, aluminumor aluminum-copper alloy.

Meanwhile, the same effects can be obtained when an additional layer isformed on the uppermost layer of the electrode brought into contact withthe bump. Meanwhile, if the electrode is formed by piling pieces made ofnot less than one metal, for example, Al, Ti, Cu, Cr and Ni or alloy ofthese metals, respectively, withstand power is raised. Thus, if theuppermost layer of the electrode is formed on a pile of pieces made of aplurality of the metals, respectively, it is possible to obtain anelectrode in which occurrence of bonding strain is restrained andwithstand power is raised.

Meanwhile, in the fourth embodiment, the auxiliary electrodes 6 a and 6b are split into two portions but may be split into any plural portions.The bump may be formed at other locations than that indicated in thefourth embodiment. Width of the beltlike input terminal lead-outelectrode and output terminal lead-out electrode 4 a and 5 a may befixed or variable.

Since hot terminals of the thus obtained SAW device 10D, for example,the input terminal lead-out electrode 4 a, the output terminal lead-outelectrode 5 a, the input terminal electrode 4 b, the output terminalelectrode 5 b and the beltlike electrode 18 are not connected to thedicing lines 28, the hot terminals are electrically dependent of thedicing lines 28, so that electrical characteristics of the SAW device10D can be beforehand measured by electrically connecting the terminalsto a necessary electrode. Namely, since electrical characteristics ofthe SAW device 10D can be measured in a wafer state preliminarily, theelectronic component 40D can be assembled by using only conformingarticles at a subsequent process by selecting characteristics prior todicing of the wafer into a plurality of the SAW devices 10D.

In accordance with the present invention as is clear from the foregoing,since inside the dicing lines 28, the comb-shaped electrode 2 and thereflector 3 are surrounded by the auxiliary electrodes 6 a and 6 b whichare electrically independent of each other and have different widthslocally and the uppermost layer of the electrode brought into contactwith the bump at least is formed by deposition, such effects that theexcellent SAW device 10D can be simply manufactured are gained in whichpotential produced by pyroelectric property of the piezoelectricsubstrate 1 can be uniformized more rapidly and more simply, bondingproperty of the electrodes is upgraded, corrosion due to bonding ofdifferent metals is restrained, withstand power is raised and breakdownof the device and deterioration of characteristics due to electrostaticdischarge or the like are eliminated.

(Fifth Embodiment)

FIG. 9 is a top plan view showing an arrangement of an electrode patternof a SAW device 10E according to a fifth embodiment of the presentinvention. In FIG. 9, parts identical with those of FIG. 6 in the fourthembodiment are designated by identical reference numerals and thedetailed description is abbreviated for the sake of brevity. Meanwhile,FIG. 9 shows an arrangement of the fifth embodiment schematically anddoes not illustrate relative ratio of respective dimensions.

FIG. 9 of the fifth embodiment is different from FIG. 6 of the fourthembodiment in that in FIG. 9, the reflector 3 is in an electrically openstate relative to the auxiliary electrodes 6 a and 6 b and the threecomb-shaped electrodes 2 are provided for each of input and outputterminals such that the two comb-shaped electrodes 2 disposed atopposite ends of the three comb-shaped electrodes 2 not only areconnected to each other by the beltlike electrode 18 but are eachconnected to each of the auxiliary electrodes 6 a and 6 b electricallyby the beltlike electrode 20.

Namely, in the fourth embodiment, the comb-shaped electrode 2 is in anelectrically open state relative to the auxiliary electrodes 6 a and 6b, while in the fifth embodiment, the three comb-shaped electrodes 2 areprovided for each of input and output terminals such that the twocomb-shaped electrodes 2 disposed at opposite ends of the threecomb-shaped electrodes 2 not only are each connected to each of theauxiliary electrodes 6 a and 6 b electrically by the beltlike electrode20 but are connected to each other by the beltlike electrode 18. The SAWdevice 10E and an electronic component 40E (FIG. 8) are manufactured inthe same manner as the fourth embodiment except for the above points.

In FIG. 9, since a corresponding one of the comb-shaped electrodes 2 iselectrically connected to each of the auxiliary electrodes 6 a and 6 bby the beltlike electrode 20 and a plurality of sets of the comb-shapedelectrodes 2 are electrically connected to each other by the beltlikeelectrode 18, electric charge generated in the comb-shaped electrodes 2,etc. is delivered to the auxiliary electrodes 6 a and 6 b through thebeltlike electrodes 20, so that potential can be uniformized, as awhole, over the wider electrodes including the auxiliary electrodes 6 aand 6 b.

Namely, since the two comb-shaped electrodes 2 disposed at the oppositeends of the three comb-shaped electrodes 2 are connected to theauxiliary electrodes 6 a and 6 b by the beltlike electrodes 20, thewider electrodes can be used as a common electrode, so that thegenerated electric charge can be uniformized over a wider area includingthe comb-shaped electrodes 2 so as to equalize potential. In addition,by connecting the comb-shaped electrodes 2 to the auxiliary electrodes 6a and 6 b by the wide electrodes, impedance can be lessened incomparison with an electrically open state, so that electrostaticdischarge is least likely to happen.

Meanwhile, effects gained by electrically connecting the comb-shapedelectrodes 2 to the auxiliary electrodes 6 a and 6 b vary according todesign of the electrode pattern. If the electrodes capable ofuniformizing potential can be connected at low impedance, the electrodesmay be linear or planar and the number of the electrodes may bearbitrary. However, it is more effective that the electrodes aredesirably planar and the number of the electrodes is large.

Meanwhile, in case the comb-shaped electrodes 2 are electricallyconnected to the auxiliary electrodes 6 a and 6 b by lines, it is notpreferable that a high-impedance portion is present in the course ofconnection paths. Hence, it is desirable that the line width is constantor becomes smaller towards an outer peripheral portion. Generally, indesign of the electrode pattern, since the dicing lines are madethinnest, it is desirable that the lines for connecting the comb-shapedelectrodes 2 to the auxiliary electrodes 6 a and 6 b are at least asthin as or thicker than the dicing lines 28.

Therefore, in comparison with the fourth embodiment, since the widerelectrodes including the comb-shaped electrodes 2 can be used as acommon electrode, the generated electric charge can be uniformized overa wider area so as to equalize potential, so that the excellent SAWdevice 10E can be simply manufactured in which breakdown of the deviceand deterioration of characteristics due to electrostatic discharge orthe like are eliminated.

In FIG. 9, “31 a” denotes a ground lead-out electrode and “31 b” denotesa ground electrode.

(Sixth Embodiment)

FIG. 10 is a top plan view showing an arrangement of an electrodepattern of a SAW device 10F according to a sixth embodiment of thepresent invention. In FIG. 10, parts identical with those of FIG. 6 inthe fourth embodiment are designated by identical reference numerals andthe detailed description is abbreviated for the sake of brevity.Meanwhile, FIG. 10 shows an arrangement of the sixth embodimentschematically and does not illustrate relative ratio of respectivedimensions.

FIG. 10 of the sixth embodiment is different from FIG. 6 of the fourthembodiment in that in FIG. 10, the reflector 3 is in an electricallyopen state relative to the auxiliary electrodes 6 a and 6 b, the threecomb-shaped electrodes 2 are provided for each of input and outputterminals such that the two comb-shaped electrodes 2 disposed atopposite ends of the three comb-shaped electrodes 2 not only areconnected to each other by the beltlike electrode 18 but are eachconnected to each of the auxiliary electrodes 6 a and 6 b electricallyby the beltlike electrode 20 and the auxiliary electrodes 6 a and 6 bare electrically connected to the dicing lines 28 by beltlike electrodes22.

Namely, in the fourth embodiment, the reflector 3 is in an electricallyopen state relative to the auxiliary electrodes 6 a and 6 b, while inthe sixth embodiment, the three comb-shaped electrodes 2 are providedfor each of input and output terminals such that the two comb-shapedelectrodes 2 disposed at opposite ends of the three comb-shapedelectrodes 2 not only are each connected to each of the auxiliaryelectrodes 6 a and 6 b electrically by the beltlike electrode 20 but areconnected to each other by the beltlike electrode 18 and the dicinglines 28 are electrically connected to the auxiliary electrodes 6 a and6 b by the beltlike electrodes 22. The SAW device 10F and an electroniccomponent 40F (FIG. 8) are manufactured in the same manner as the fourthembodiment except for the above points.

In FIG. 10, since the dicing lines 28 are electrically connected to theauxiliary electrodes 6 a and 6 b by the beltlike electrodes 22, electriccharge generated in the piezoelectric substrate 1 can be uniformized, asa whole, over the electrodes including the auxiliary electrodes 6 a and6 b and the dicing lines 28 so as to equalize potential.

Namely, since the dicing lines 28 are electrically connected to theauxiliary electrodes 6 a and 6 b by the beltlike electrodes 22, thewider electrodes including the dicing lines 28 can be used as a commonelectrode, so that the electric charge generated in the piezoelectricsubstrate 1 can be uniformized over a wider area including thecomb-shaped electrodes 2 so as to equalize potential. In addition, byconnecting the dicing lines 28 to the auxiliary electrodes 6 a and 6 bby the wide electrodes, impedance can be lessened in comparison with anelectrically open state, so that electrostatic discharge is least likelyto happen.

Meanwhile, effects gained by electrically connecting the dicing lines 28to the auxiliary electrodes 6 a and 6 b vary according to design of theelectrode pattern. If the electrodes capable of uniformizing potentialcan be connected at low impedance, the electrodes may be linear orplanar and the number of the electrodes may be arbitrary. However, it ismore effective that the electrodes are desirably planar and the numberof the electrodes is large.

Meanwhile, in case the dicing lines 28 are electrically connected to theauxiliary electrodes 6 a and 6 b by lines, it is not preferable that ahigh-impedance portion is present in the course of connection paths.Hence, it is desirable that the line width becomes smaller towards anouter peripheral portion. Generally, in design of the electrode pattern,since the dicing lines 28 are made thinnest, it is desirable that thelines for connecting the dicing lines 28 to the auxiliary electrodes 6 aand 6 b are at least as thin as or thicker than the dicing lines 28.

Therefore, in comparison with the fourth embodiment, since the threecomb-shaped electrodes 2 are provided such that the two comb-shapedelectrodes 2 disposed at opposite ends of the three comb-shapedelectrodes 2, the auxiliary electrodes 6 a and 6 b and the dicing lines28 are connected to one another electrically by the beltlike electrodes18, 20 and 22, the wider electrodes can be used as a common electrode.Hence, since influence of potential exerted by electric charge generatedat respective portions can be lessened further, the excellent SAW device10F can be simply manufactured in which breakdown of the device anddeterioration of characteristics due to electrostatic discharge or thelike are eliminated.

(Seventh Embodiment)

FIG. 11 is a top plan view showing an arrangement of an electrodepattern of a SAW device 10G according to a seventh embodiment of thepresent invention. In FIG. 11, parts identical with those of FIG. 6 inthe fourth embodiment are designated by identical reference numerals andthe detailed description is abbreviated for the sake of brevity.Meanwhile, FIG. 11 shows an arrangement of the seventh embodimentschematically and does not illustrate relative ratio of respectivedimensions.

FIG. 11 of the seventh embodiment is different from FIG. 6 of the fourthembodiment in that in FIG. 11, the three comb-shaped electrodes 2 areprovided for each of input and output terminals such that the twocomb-shaped electrodes 2 disposed at opposite ends of the threecomb-shaped electrodes 2 not only are each connected to each of theauxiliary electrodes 6 a and 6 b electrically by the beltlike electrode20 but are connected to each other by the beltlike electrode 18, thereflector 3 is electrically connected to the auxiliary electrodes 6 aand 6 b by the beltlike electrodes 17 and the dicing lines 28 areprovided outside the comb-shaped electrode 2 and the reflector 3 so asto be electrically connected to the auxiliary electrodes 6 a and 6 b bythe beltlike electrodes 22.

Namely, in the fourth embodiment, the comb-shaped electrode 2, thereflector 3 and the dicing lines 28 are in an electrically open state,while in the seventh embodiment, the dicing lines 28, the auxiliaryelectrodes 6 a and 6 b, the two comb-shaped electrodes 2 disposed at theopposite ends of the three comb-shaped electrodes 2 and the reflector 3are electrically connected to one another by the beltlike electrodes 17,18, 20 and 22. The SAW device 10G and an electronic component 40G (FIG.8) are manufactured in the same manner as the fourth embodiment exceptfor the above points.

In FIG. 11, since the dicing lines 28, the auxiliary electrodes 6 a and6 b, the two comb-shaped electrodes 2 disposed at the opposite ends ofthe three comb-shaped electrodes 2 and the reflector 3 are electricallyconnected to one another by the beltlike electrodes 17, 18, 20 and 22,electric charge generated in the piezoelectric substrate 1 can beuniformized over the whole electrodes including the two comb-shapedelectrodes disposed at the opposite ends of the three comb-shapedelectrodes 2, the reflector 3, the auxiliary electrodes 6 a and 6 b andthe dicing lines 28 so as to equalize potential.

Namely, since the dicing lines 28, the auxiliary electrodes 6 a and 6 b,the two comb-shaped electrodes 2 disposed at the opposite ends of thethree comb-shaped electrodes 2 and the reflector 3 are electricallyconnected to one another by the beltlike electrodes 17, 18, 20 and 22,not only electric charge can be uniformized, as a whole, over the widerelectrodes including the dicing lines 28, the auxiliary electrodes 6 aand 6 b, the two comb-shaped electrodes 2 disposed at the opposite endsof the three comb-shaped electrodes 2 and the reflector 3 so as toreduce potential difference but impedance between common electrodes canbe lessened in comparison with an electrically open state.

Meanwhile, effects gained by electrically connecting the dicing lines28, the auxiliary electrodes 6 a and 6 b, the two comb-shaped electrodes2 disposed at the opposite ends of the three comb-shaped electrodes 2and the reflector 3 vary according to design of the electrode pattern.If the electrodes capable of uniformizing potential can be connected atlow impedance, the electrodes may be linear or planar and the number ofthe electrodes may be arbitrary. However, it is more effective that theelectrodes are desirably planar and the number of the electrodes islarge.

Therefore, in comparison with the fourth embodiment, since the twocomb-shaped electrodes 2 disposed at the opposite ends of the threecomb-shaped electrodes 2, the reflector 3, the auxiliary electrodes 6 aand 6 b and the dicing lines 28 are electrically connected to oneanother, the wider electrodes can be used as a common electrode. Hence,since potential difference produced at respective portions can belessened further, the excellent SAW device 10G can be simplymanufactured in which breakdown of the device and deterioration ofcharacteristics due to electrostatic discharge or the like areeliminated.

(Eighth Embodiment)

FIG. 12 is a top plan view showing an arrangement of an electrodepattern of a SAW device 10H according to an eighth embodiment of thepresent invention. In FIG. 12, parts identical with those of FIG. 6 inthe fourth embodiment are designated by identical reference numerals andthe detailed description is abbreviated for the sake of brevity.Meanwhile, FIG. 12 shows an arrangement of the eighth embodimentschematically and does not illustrate relative ratio of respectivedimensions.

FIG. 12 of the eighth embodiment is different from FIG. 6 of the fourthembodiment in that in FIG. 12, the reflector is formed by a meander lineand is electrically connected to the comb-shaped electrode 2.

Namely, in the fourth embodiment, the comb-shaped electrode 2 and thereflector 3 are in an electrically open state, while in the eighthembodiment, the comb-shaped electrode 2 and the reflector 19 formed bythe meander line are electrically connected to each other and the dicinglines 28 are provided outside the auxiliary electrodes 6 a and 6 b. TheSAW device 10H and an electronic component 40H (FIG. 8) are manufacturedin the same manner as the fourth embodiment except for the above points.

In FIG. 12, the reflector 19 formed by the meander line is electricallyconnected to the comb-shaped electrode 2 and signals in use aretransmitted therebetween in DC or at low frequencies. However, in ahigh-frequency band for operating the SAW device 10H, impedance of themeander line rises and thus, the meander line is substantially set in anopen state relative to the comb-shaped electrode 2.

Meanwhile, since a common electrode portion can be enlarged byelectrically connecting the comb-shaped electrode 2 and the reflector 19formed by the meander line, electric charge generated by pyroelectricproperty of the piezoelectric substrate 1 can be uniformized over awider electrode or a longer electrode as a whole, so that potentialdifference produced at respective portions can be lessened.

Namely, since the reflector 19 formed by the meander line iselectrically connected to the comb-shaped electrode 2, the reflector 19and the comb-shaped electrode 2 are set in a substantially open state atoperating frequency so as to not only eliminate malfunctions but enlargean electrically connected common electrode portion, so that electriccharge generated in the piezoelectric substrate 1 can be uniformizedover the whole electrodes including the reflector 19 and the comb-shapedelectrode 2 so as to equalize potential.

Meanwhile, the auxiliary electrodes 6 a and 6 b and the dicing lines 28may be electrically connected to each other by at least one linear orbeltlike electrode such that a common electrode for uniformizingproduced potential is further enlarged.

Therefore, in comparison with the fourth embodiment, since the reflector19 formed by the meander line is electrically connected to thecomb-shaped electrode 2, the reflector 19 and the comb-shaped electrode2 are set in a substantially open state at operating frequency so as tonot only eliminate malfunctions but enlarge an electrically connectedcommon electrode portion, so that electric charge generated in thepiezoelectric substrate 1 can be uniformized over the whole electrodesincluding the reflector 19 and the comb-shaped electrode 2 so as toequalize potential. Hence, since potential difference produced atrespective portions can be lessened further, the excellent SAW device10H can be simply manufactured in which breakdown of the device anddeterioration of characteristics due to electrostatic discharge or thelike are eliminated.

In accordance with the first to third embodiments of the presentinvention as is clear from the foregoing description, since thecomb-shaped electrode and the reflector are surrounded by the auxiliaryelectrodes, potential produced by pyroelectric property of thepiezoelectric substrate can be uniformized more rapidly and more simplyeven after the wafer has been cut into a plurality of the SAW devices,so that the excellent SAW device can be manufactured simply in whichbreakdown of the device and deterioration of characteristics due toelectrostatic discharge or the like are eliminated.

Meanwhile, in accordance with the fourth to eighth embodiments of thepresent invention, since the comb-shaped electrode and the reflector aresurrounded by the auxiliary electrodes inside the dicing lines,potential produced by pyroelectric property of the piezoelectricsubstrate can be uniformized more rapidly and more simply even after thewafer has been cut into a plurality of the SAW devices, so that theexcellent SAW device can be manufactured simply in which breakdown ofthe device and deterioration of characteristics due to electrostaticdischarge or the like are eliminated.

1. A surface acoustic wave (SAW) device comprising: first and secondcomb-shaped electrodes which are provided axially opposite to each otheron a piezoelectric substrate; a pair of first reflectors and a pair ofsecond reflectors which are provided, on the piezoelectric substrate, atopposite sides of the first comb-shaped electrode along propagationdirection of a surface wave generated from the first comb-shapedelectrode and at opposite sides of the second comb-shaped electrodealong a propagation direction of a surface wave generated from thesecond comb-shaped electrode, respectively, and are electricallyisolated from the first and second comb-shaped electrodes, respectively;and a plurality of auxiliary electrodes for surrounding the first andsecond comb-shaped electrodes, the pair of first reflectors and the pairof second reflectors, which are electrically independent of each otherand have different widths locally.
 2. A SAW device as claimed in claim1, wherein the auxiliary electrodes are each used as a ground electrode.3. A SAW device as claimed in claim 1, wherein the auxiliary electrodesare disposed substantially equivalently.
 4. A SAW device as claimed inclaim 1, further comprising: a beltlike input terminal lead-outelectrode connected to the first comb-shaped electrode and a beltlikeoutput terminal lead-out electrode connected to the second comb-shapedelectrode; an input terminal electrode which is connected to the inputterminal lead-out electrode; and an output terminal electrode which isconnected to the output terminal lead-out electrode.
 5. A SAW device asclaimed in claim 4, wherein the input terminal lead-out electrode andthe output terminal lead-out electrode are symmetric about a centralaxis between the first and second comb-shaped electrodes and are madesubstantially equal in area, and the input terminal electrode and theoutput terminal electrode are symmetric about a central axis between thefirst and second comb-shaped electrodes and are made substantially equalin area.
 6. A SAW device as claimed in claim 1, wherein at least aportion of the reflectors is electrically connected to the auxiliaryelectrodes.
 7. A SAW device as claimed in claim 6, wherein eachreflector is electrically connected to one of the auxiliary electrodesby a linear or beltlike electrode.
 8. A SAW device as claimed in claim1, wherein the reflectors are set in an electrically open state relativeto the auxiliary electrodes.
 9. A surface acoustic wave (SAW) devicecomprising: a comb-shaped electrode which is provided on a piezoelectricsubstrate; a pair of reflectors which are provided, on the piezoelectricsubstrate, at opposite sides of the comb-shaped electrode along apropagation direction of a surface wave generated from the comb-shapedelectrode; a plurality of auxiliary electrodes for surrounding thecomb-shaped electrode and the pair of reflectors, which are electricallyindependent of each other and have different widths locally; a beltlikeinput terminal lead-out electrode and a beltlike output terminallead-out electrode which are each connected to the comb-shapedelectrode; an input terminal electrode which is connected to the inputterminal lead-out electrode; and an output terminal electrode which isconnected to the output terminal lead-out electrode, wherein eachreflector is formed by a meander line and is electrically connected tothe comb-shaped electrode, and wherein the input terminal lead-outelectrode and the output terminal lead-out electrode are symmetric andare made substantially equal in area, and the input terminal electrodeand the output terminal electrode are symmetric and are madesubstantially equal in area.
 10. An electronic component comprising: a)a surface acoustic wave (SAW) device including: first and secondcomb-shaped electrodes which are provided axially opposite to each otheron a piezoelectric substrate, a pair of first and a pair of secondreflectors which are provided, on the piezoelectric substrate, atopposite sides of the first comb-shaped electrode along a propagationdirection of a surface wave generated from the first comb-shapedelectrode and at opposite sides of the second comb-shaped electrodealong a propagation direction of a surface wave generated from thesecond comb-shaped electrode, respectively, and are electricallyisolated from the first and second comb-shaped electrodes, respectively,a plurality of auxiliary electrodes for surrounding the first and secondcomb-shaped electrodes, the pair of first reflectors and the pair ofsecond reflectors, which are electrically independent of each other andhave different widths locally, a beltlike input terminal lead-outelectrode connected to the first comb-shaped electrode and a beltlikeoutput terminal lead-out electrode connected to the second comb-shapedelectrode, an input terminal electrode electrically connected to theinput terminal lead-out electrode and an output terminal electrodeelectrically connected to the output terminal lead-out electrode; and b)a base member which has the SAW device mounted thereon and is sealed.11. An electronic component comprising: a) a surface acoustic wave (SAW)device including: a comb-shaped electrode which is provided on apiezoelectric substrate; a pair of reflectors which are provided, on thepiezoelectric substrate, at opposite sides of the comb-shaped electrodealong a propagation direction of a surface wave generated from thecomb-shaped electrode; a plurality of auxiliary electrodes forsurrounding the comb-shaped electrode and the pair of reflectors, whichare electrically independent of each other and have different widthslocally; a beltlike input terminal lead-out electrode and a beltlikeoutput terminal lead-out electrode which are each connected to thecomb-shaped electrode; an input terminal electrode which is connected tothe input terminal lead-out electrode; and an output terminal electrodewhich is connected to the output terminal lead-out electrode, whereineach reflector is formed by a meander line and is electrically connectedto the comb-shaped electrode, and the input terminal lead-out electrodeand the output terminal lead-out electrode are symmetric and are madesubstantially equal in area, and the input terminal electrode and theoutput terminal electrode are symmetric and are made substantially equalin area; and b) a base member which has the SAW device mounted thereonis sealed.